A device which provides a function called link aggregation (LA) is known. LA is a technique which bundles plural physical ports so that they are used as one logical port between two apparatuses. A device corresponding to LA selects an output physical port belonging to a LA port from identification information (ID) which specifies a flow, such as a VLAN (Virtual LAN) tag and MAC.
Some MPLS (Multi-Protocol Label Switching) transmission apparatuses determine a MPLS LSP (Label Switching Path) connection from, for example, a VLAN. An MPLS transmission apparatus provided with a maintenance function by MPLS OAM (Operations, Administration and Maintenance) monitors end-to-end connectivity by periodically forwarding a connectivity verification (CV) frame. When the CV frame is not received, each interface unit changes over the operating system from working to protection.    Nonpatent document 1: ITU-T Recommendation Y.1710 SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE AND INTERNET PROTOCOL ASPECTS, Internet Protocol Aspects-Operation, Administration and Maintenance    Nonpatent document 2: ITU-T Recommendation Y.1720 SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE AND INTERNET PROTOCOL ASPECTS, Internet Protocol Aspects—Operation, Administration and Maintenance Protection switching for MPLS networks    Nonpatent document 3: IEEE Standard for information technology telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements, Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications, Section 3, Chapter 43, pp. 285-350.